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+SSH-KEYSCAN(1)             OpenBSD Reference Manual             SSH-KEYSCAN(1)
+
+NAME
+     ssh-keyscan - gather ssh public keys
+
+SYNOPSIS
+     ssh-keyscan [-46Hv] [-f file] [-p port] [-T timeout] [-t type]
+                 [host | addrlist namelist] [...]
+
+DESCRIPTION
+     ssh-keyscan is a utility for gathering the public ssh host keys of a num-
+     ber of hosts.  It was designed to aid in building and verifying
+     ssh_known_hosts files.  ssh-keyscan provides a minimal interface suitable
+     for use by shell and perl scripts.
+
+     ssh-keyscan uses non-blocking socket I/O to contact as many hosts as pos-
+     sible in parallel, so it is very efficient.  The keys from a domain of
+     1,000 hosts can be collected in tens of seconds, even when some of those
+     hosts are down or do not run ssh.  For scanning, one does not need login
+     access to the machines that are being scanned, nor does the scanning pro-
+     cess involve any encryption.
+
+     The options are as follows:
+
+     -4      Forces ssh-keyscan to use IPv4 addresses only.
+
+     -6      Forces ssh-keyscan to use IPv6 addresses only.
+
+     -f file
+             Read hosts or addrlist namelist pairs from this file, one per
+             line.  If - is supplied instead of a filename, ssh-keyscan will
+             read hosts or addrlist namelist pairs from the standard input.
+
+     -H      Hash all hostnames and addresses in the output.  Hashed names may
+             be used normally by ssh and sshd, but they do not reveal identi-
+             fying information should the file's contents be disclosed.
+
+     -p port
+             Port to connect to on the remote host.
+
+     -T timeout
+             Set the timeout for connection attempts.  If timeout seconds have
+             elapsed since a connection was initiated to a host or since the
+             last time anything was read from that host, then the connection
+             is closed and the host in question considered unavailable.  De-
+             fault is 5 seconds.
+
+     -t type
+             Specifies the type of the key to fetch from the scanned hosts.
+             The possible values are ``rsa1'' for protocol version 1 and
+             ``rsa'' or ``dsa'' for protocol version 2.  Multiple values may
+             be specified by separating them with commas.  The default is
+             ``rsa1''.
+
+     -v      Verbose mode.  Causes ssh-keyscan to print debugging messages
+             about its progress.
+
+SECURITY
+     If an ssh_known_hosts file is constructed using ssh-keyscan without veri-
+     fying the keys, users will be vulnerable to man in the middle attacks.
+     On the other hand, if the security model allows such a risk, ssh-keyscan
+     can help in the detection of tampered keyfiles or man in the middle at-
+     tacks which have begun after the ssh_known_hosts file was created.
+
+FILES
+     Input format:
+
+     1.2.3.4,1.2.4.4 name.my.domain,name,n.my.domain,n,1.2.3.4,1.2.4.4
+
+     Output format for rsa1 keys:
+
+     host-or-namelist bits exponent modulus
+
+     Output format for rsa and dsa keys:
+
+     host-or-namelist keytype base64-encoded-key
+
+     Where keytype is either ``ssh-rsa'' or ``ssh-dss''.
+
+     /etc/ssh/ssh_known_hosts
+
+EXAMPLES
+     Print the rsa1 host key for machine hostname:
+
+     $ ssh-keyscan hostname
+
+     Find all hosts from the file ssh_hosts which have new or different keys
+     from those in the sorted file ssh_known_hosts:
+
+     $ ssh-keyscan -t rsa,dsa -f ssh_hosts | \
+             sort -u - ssh_known_hosts | diff ssh_known_hosts -
+
+SEE ALSO
+     ssh(1), sshd(8)
+
+AUTHORS
+     David Mazieres <dm@lcs.mit.edu> wrote the initial version, and Wayne
+     Davison <wayned@users.sourceforge.net> added support for protocol version
+     2.
+
+BUGS
+     It generates "Connection closed by remote host" messages on the consoles
+     of all the machines it scans if the server is older than version 2.9.
+     This is because it opens a connection to the ssh port, reads the public
+     key, and drops the connection as soon as it gets the key.
+
+OpenBSD 4.2                      June 5, 2007                                2